This is a great site! I found this site before I entered the N-Prize and started the team. I was in aw of the photos. Check out Sondemonitor http://www.coaa.co.uk/sondemonitor.htm It is a cheaper solution if you can find a rs92-sgp radiosonde on ebay or on the sondemonitor yahoo group (thats were we got 2 of em) then all you need is a scanner and a laptop with a cheap GPS module (about $30) on ebay. It is the cheapest way to go I believe. We plan to launch one this week or early next week.

Back in 2007 we (ASLI) investigated using one of the LEO constellations as a method to receive telemetry from a rocket. This has been successfully trialed by NASA some years ago using a commercially sourced Globalstar OEM data modem, launched in a sounding rocket. I know that the Qualcomm modems are out of the price range for N-prize, but perhaps some of the simplex offerings for Orbcomm or Iridium might be cheaper.

Use of existing space base based network would negate the need for your own ground based tracking stations and allow you to pull your data through the Internet to a laptop computer , pretty much anywhere in the world..If this was going onto your balloon platform you could even look at using Immarsat RBGAN, which is full speed broadband capable. And then using a radio link between the balloon platform and the rocket (900mhz or 2ghz), at 30km alt your over the horizon range would be incredible.